DWARF parsing and writing support using LLVM (#2520)

This imports LLVM code for DWARF handling. That code has the
Apache 2 license like us. It's also the same code used to
emit DWARF in the common toolchain, so it seems like a safe choice.

This adds two passes: --dwarfdump which runs the same code LLVM
runs for llvm-dwarfdump. This shows we can parse it ok, and will
be useful for debugging. And --dwarfupdate writes out the DWARF
sections (unchanged from what we read, so it just roundtrips - for
updating we need #2515).

This puts LLVM in thirdparty which is added here.

All the LLVM code is behind USE_LLVM_DWARF, which is on
by default, but off in JS for now, as it increases code size by 20%.

This current approach imports the LLVM files directly. This is not
how they are intended to be used, so it required a bunch of
local changes - more than I expected actually, for the platform-specific
stuff. For now this seems to work, so it may be good enough, but
in the long term we may want to switch to linking against libllvm.
A downside to doing that is that binaryen users would need to
have an LLVM build, and even in the waterfall builds we'd have a
problem - while we ship LLVM there anyhow, we constantly update
it, which means that binaryen would need to be on latest llvm all
the time too (which otherwise, given DWARF is quite stable, we
might not need to constantly update).

An even larger issue is that as I did this work I learned about how
DWARF works in LLVM, and while the reading code is easy to
reuse, the writing code is trickier. The main code path is heavily
integrated with the MC layer, which we don't have - we might want
to create a "fake MC layer" for that, but it sounds hard. Instead,
there is the YAML path which is used mostly for testing, and which
can convert DWARF to and from YAML and from binary. Using
the non-YAML parts there, we can convert binary DWARF to
the YAML layer's nice Info data, then convert that to binary. This
works, however, this is not the path LLVM uses normally, and it
supports only some basic DWARF sections - I had to add ranges
support, in fact. So if we need more complex things, we may end
up needing to use the MC layer approach, or consider some other
DWARF library. However, hopefully that should not affect the core
binaryen code which just calls a library for DWARF stuff.

Helps #2400

1 files changed, 214 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/Object/SymbolicFile.h b/third_party/llvm-project/include/llvm/Object/SymbolicFile.h
new file mode 100644
index 000000000..1398fa134
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/Object/SymbolicFile.h
@@ -0,0 +1,214 @@
+//===- SymbolicFile.h - Interface that only provides symbols ----*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the SymbolicFile interface.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_OBJECT_SYMBOLICFILE_H
+#define LLVM_OBJECT_SYMBOLICFILE_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/BinaryFormat/Magic.h"
+#include "llvm/Object/Binary.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Format.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include <cinttypes>
+#include <cstdint>
+#include <cstring>
+#include <iterator>
+#include <memory>
+#include <system_error>
+
+namespace llvm {
+namespace object {
+
+union DataRefImpl {
+  // This entire union should probably be a
+  // char[max(8, sizeof(uintptr_t))] and require the impl to cast.
+  struct {
+    uint32_t a, b;
+  } d;
+  uintptr_t p;
+
+  DataRefImpl() { std::memset(this, 0, sizeof(DataRefImpl)); }
+};
+
+template <typename OStream>
+OStream& operator<<(OStream &OS, const DataRefImpl &D) {
+  OS << "(" << format("0x%08" PRIxPTR, D.p) << " (" << format("0x%08x", D.d.a)
+     << ", " << format("0x%08x", D.d.b) << "))";
+  return OS;
+}
+
+inline bool operator==(const DataRefImpl &a, const DataRefImpl &b) {
+  // Check bitwise identical. This is the only legal way to compare a union w/o
+  // knowing which member is in use.
+  return std::memcmp(&a, &b, sizeof(DataRefImpl)) == 0;
+}
+
+inline bool operator!=(const DataRefImpl &a, const DataRefImpl &b) {
+  return !operator==(a, b);
+}
+
+inline bool operator<(const DataRefImpl &a, const DataRefImpl &b) {
+  // Check bitwise identical. This is the only legal way to compare a union w/o
+  // knowing which member is in use.
+  return std::memcmp(&a, &b, sizeof(DataRefImpl)) < 0;
+}
+
+template <class content_type>
+class content_iterator
+    : public std::iterator<std::forward_iterator_tag, content_type> {
+  content_type Current;
+
+public:
+  content_iterator(content_type symb) : Current(std::move(symb)) {}
+
+  const content_type *operator->() const { return &Current; }
+
+  const content_type &operator*() const { return Current; }
+
+  bool operator==(const content_iterator &other) const {
+    return Current == other.Current;
+  }
+
+  bool operator!=(const content_iterator &other) const {
+    return !(*this == other);
+  }
+
+  content_iterator &operator++() { // preincrement
+    Current.moveNext();
+    return *this;
+  }
+};
+
+class SymbolicFile;
+
+/// This is a value type class that represents a single symbol in the list of
+/// symbols in the object file.
+class BasicSymbolRef {
+  DataRefImpl SymbolPimpl;
+  const SymbolicFile *OwningObject = nullptr;
+
+public:
+  enum Flags : unsigned {
+    SF_None = 0,
+    SF_Undefined = 1U << 0,      // Symbol is defined in another object file
+    SF_Global = 1U << 1,         // Global symbol
+    SF_Weak = 1U << 2,           // Weak symbol
+    SF_Absolute = 1U << 3,       // Absolute symbol
+    SF_Common = 1U << 4,         // Symbol has common linkage
+    SF_Indirect = 1U << 5,       // Symbol is an alias to another symbol
+    SF_Exported = 1U << 6,       // Symbol is visible to other DSOs
+    SF_FormatSpecific = 1U << 7, // Specific to the object file format
+                                 // (e.g. section symbols)
+    SF_Thumb = 1U << 8,          // Thumb symbol in a 32-bit ARM binary
+    SF_Hidden = 1U << 9,         // Symbol has hidden visibility
+    SF_Const = 1U << 10,         // Symbol value is constant
+    SF_Executable = 1U << 11,    // Symbol points to an executable section
+                                 // (IR only)
+  };
+
+  BasicSymbolRef() = default;
+  BasicSymbolRef(DataRefImpl SymbolP, const SymbolicFile *Owner);
+
+  bool operator==(const BasicSymbolRef &Other) const;
+  bool operator<(const BasicSymbolRef &Other) const;
+
+  void moveNext();
+
+  Error printName(raw_ostream &OS) const;
+
+  /// Get symbol flags (bitwise OR of SymbolRef::Flags)
+  uint32_t getFlags() const;
+
+  DataRefImpl getRawDataRefImpl() const;
+  const SymbolicFile *getObject() const;
+};
+
+using basic_symbol_iterator = content_iterator<BasicSymbolRef>;
+
+class SymbolicFile : public Binary {
+public:
+  SymbolicFile(unsigned int Type, MemoryBufferRef Source);
+  ~SymbolicFile() override;
+
+  // virtual interface.
+  virtual void moveSymbolNext(DataRefImpl &Symb) const = 0;
+
+  virtual Error printSymbolName(raw_ostream &OS, DataRefImpl Symb) const = 0;
+
+  virtual uint32_t getSymbolFlags(DataRefImpl Symb) const = 0;
+
+  virtual basic_symbol_iterator symbol_begin() const = 0;
+
+  virtual basic_symbol_iterator symbol_end() const = 0;
+
+  // convenience wrappers.
+  using basic_symbol_iterator_range = iterator_range<basic_symbol_iterator>;
+  basic_symbol_iterator_range symbols() const {
+    return basic_symbol_iterator_range(symbol_begin(), symbol_end());
+  }
+
+  // construction aux.
+  static Expected<std::unique_ptr<SymbolicFile>>
+  createSymbolicFile(MemoryBufferRef Object, llvm::file_magic Type,
+                     LLVMContext *Context);
+
+  static Expected<std::unique_ptr<SymbolicFile>>
+  createSymbolicFile(MemoryBufferRef Object) {
+    return createSymbolicFile(Object, llvm::file_magic::unknown, nullptr);
+  }
+  static Expected<OwningBinary<SymbolicFile>>
+  createSymbolicFile(StringRef ObjectPath);
+
+  static bool classof(const Binary *v) {
+    return v->isSymbolic();
+  }
+};
+
+inline BasicSymbolRef::BasicSymbolRef(DataRefImpl SymbolP,
+                                      const SymbolicFile *Owner)
+    : SymbolPimpl(SymbolP), OwningObject(Owner) {}
+
+inline bool BasicSymbolRef::operator==(const BasicSymbolRef &Other) const {
+  return SymbolPimpl == Other.SymbolPimpl;
+}
+
+inline bool BasicSymbolRef::operator<(const BasicSymbolRef &Other) const {
+  return SymbolPimpl < Other.SymbolPimpl;
+}
+
+inline void BasicSymbolRef::moveNext() {
+  return OwningObject->moveSymbolNext(SymbolPimpl);
+}
+
+inline Error BasicSymbolRef::printName(raw_ostream &OS) const {
+  return OwningObject->printSymbolName(OS, SymbolPimpl);
+}
+
+inline uint32_t BasicSymbolRef::getFlags() const {
+  return OwningObject->getSymbolFlags(SymbolPimpl);
+}
+
+inline DataRefImpl BasicSymbolRef::getRawDataRefImpl() const {
+  return SymbolPimpl;
+}
+
+inline const SymbolicFile *BasicSymbolRef::getObject() const {
+  return OwningObject;
+}
+
+} // end namespace object
+} // end namespace llvm
+
+#endif // LLVM_OBJECT_SYMBOLICFILE_H